Various inkjet printing arrangements are known in the art and include both thermally actuated printheads and mechanically actuated printheads. Thermal actuated printheads tend to use resistive elements or the like to achieve ink expulsion, while mechanically actuated printheads tend to use piezoelectric transducers or the like.
A representative thermal inkjet printhead has a plurality of thin film resistors provided on a semiconductor substrate. A nozzle plate and a barrier layer are provided on the substrate and define the firing chambers about each of the resistors. Propagation of a current or a “fire signal” through a resistor causes ink in the corresponding firing chamber to be heated and expelled through the corresponding nozzle.
Ink is typically delivered to the firing chamber through a feed slot that is machined in the semiconductor substrate. The substrate usually has a rectangular shape, with the slot disposed longitudinally therein. Resistors are typically arranged in rows located on both sides of the slot and are preferably spaced approximately equal distances from the slot so that the ink channel length at each resistor is approximately equal. The width of the print swath achieved by one pass of a printhead is approximately equal to the length of the resistor rows, which in turn is approximately equal to the length of the slot.
Feed slots have typically been formed by sand drilling (also known as “sand slotting”). This method is a rapid, relatively simple and scalable process. The sand blasting method is capable of forming an opening in a substrate with a high degree of accuracy, while generally avoiding substantial damage to surrounding components and materials. Also, it is capable of cutting openings in many different types of substrates without the generation of excessive heat. Furthermore, it allows for improved relative placement accuracies during the production process.
While sand slotting affords these apparent benefits, sand slotting is also disadvantageous in that it may cause microcracks in the semiconductor substrate that significantly reduce the substrates fracture strength, resulting in significant yield loss due to cracked die. Low fracture strength also limits substrate length which in turn adversely impacts print swath height and overall print speed.
In addition, sand slotting typically causes chips to the substrate on both the input and output side of the slot. This chipping causes two separate issues. Normally the chipping is tens of microns large and limits how close the firing chamber can be placed to the edge of the slot. Occasionally the chipping is larger and causes yield loss in the manufacturing process. The chipping problem is more prevalent as the desired slot length increases and the desired slot width decreases.